1. Field of the Invention
The present invention relates to a gas-filled insulating bushing and more particularly to a gas-filled insulating bushing which is superior in safety and capable of preventing fragments of a porcelain tube from widely flying or scattering when it is exploded by a dielectric breakdown in the air.
2. Description of the Prior Art
In general, as sulfur hexafluoride gas (SF.sub.6 gas) is superior in arc suppressing capacity and insulating performance, it has been widely used for gas-filled circuit breakers or gas-filled insulating switching devices. Particularly, it has been used in bushings at the outputs of such devices. In this case, as shown in FIG. 1, a center conductor 1 is surrounded by a porcelain tube 2 whose inner cavity is sealingly filled with a gas in an air tight manner. The gas pressure in the bushing is usually 2-5 kg/cm.sup.2 g which provides a sufficient safety factor for the breaking down pressure of the porcelain tube under usual operating conditions. However, when the porcelain tube is damaged due to collision of foreign matter or flashing of the tube by extraordinary voltage, fragments of the tube would widely scatter due to the gas pressure in the tube and would further break instruments or equipment neighboring the bushing.
In order to avoid such an occurrence, a prior art gas-filled insulating bushing as shown in FIG. 2 has been proposed, wherein a thick tubular insulating partition 15 consisting of a glass fiber or glass cloth and a thermosetting synthetic resin integrally set therewith is arranged centrally about a center conductor 1 in a porcelain tube 2 to divide a cavity in the tube into two chambers, one in the insulating partition 15 for accommodating the greater part of the inner pressure of the bushing and the other outer chamber between the insulating partition 15 and the porcelain tube 2 for receiving a gas in the order of the atmospheric pressure, thereby preventing an explosion of the porcelain tube.
With such an arrangement including the insulating partition supporting the greater part of the inner pressure, however, a large and high strength insulating partition is required for high voltage. The larger the insulating partition, the more difficult it is to obtain a partition stable in strength. Moreover, greater and more complicated procedures are required for manufacturing such insulating partitions, so that the partitions obtained become expensive. In addition, the increased weight of the insulating partition requires a much firmer mounting portion thereof and the bushing itself becomes larger.
On the other hand, disasters caused by the scattered fragments of porcelain tubes damaged due to flashing of an instrument have become serious because the voltages used in systems have been going higher and higher. Under these circumstances, it has been necessary to develop gas-filled insulating bushings which are simple in construction and capable of preventing fragments of porcelain tubes from widely scattering even if the tubes are damaged due to flashing.